How Many Trees Will Redeem My Lifetime Miles?

I have a very conflicted relationship with airplane travel. On the one hand, my lifestyle — both personal and professional — depends on it and, in particular, on long-distance flights. On the other, I hate that airplanes are so damn bad for the environment, and that there are no signs of them getting any better any time soon.

Recently, due to inevitable family circumstances, I came into possession of a relatively large piece of land in Portugal, some of which had been woodland before a series of fires completely ruined it. I’m looking at this at as opportunity for redemption. If I replant these areas, will it be enough to offset my lifetime CO2-e due to my frequent air travel? That’d be really nice.

To answer my question, I need two estimates. The first one is the estimate of how many miles I flew in airplanes so far. That can then be converted to CO2 emissions (CO2-e) using one of the many calculators out there. The second one is an estimate for how much CO2 a tree absorbs over its lifetime.

Here are the calculations.

How Much CO2 Did I Emit Until Now?

My United Frequent Flyer account, which I have since 1997, shows ~580,000 lifetime miles. This accounts for all the flights I registered with United and Continental (they merged). But this is a severe lower bound for my real miles. For one, there was a time when I often forgot to enter my frequent flyer number. Then, I also traveled a lot with other companies, such as KLM, Lufthansa, TAP Air Portugal, British Airways, Air France, and others. My estimate of my real lifetime miles is double of what’s on my United account. So about 1.2 million miles, the vast majority of which have been long-distance flights. This is, roughly, 2 million kilometers.

Using this calculator, and typing a few common trips, it appears that my typical flights emit 0.164Kg of CO2 per Km. So…

I have, so far, been responsible for the emission of 0.164 x 2,000,000 = 328 tons of CO2. Yikes! Will I ever be able to clean this up?

How Much CO2 Can a Tree Absorb?

If CO2-e estimates of flights are tricky, estimates of CO2 absorption by trees are even trickier! First of all, there is an enormous variety of trees, and they all perform differently. Then, their performance also depends on their environment. Etc etc. But even with all these sources of uncertainty, and all these disclaimers, I’m plowing ahead towards an estimate. I’m using this web site of tree facts to focus on one single sentence in there:

A tree can absorb as much as 48 pounds of carbon dioxide per year and can sequester 1 ton of carbon dioxide by the time it reaches 40 years old.

Let me focus on a plan of planting trees, with good maintenance, for a long time. Let’s use that estimate of 1 ton of CO2 for the lifetime of a tree, approximately 40 years, which may be too optimistic. That means that I would have to plant 328 trees, and maintain them alive and well, for 40 years in order to clean up the CO2-e from my air travel.

But, as I said above, that estimate seems a bit optimistic. Also, I’m not sure I will be alive in 40 years, and I would like to move on to the next life knowing that I left this one carbon neutral. So, let’s use a lower estimate of 500Kg of CO2 in a period of 20 years. This results in needing to plant 328/0.5 = 656 trees, and keep them alive and well for 20 years.

And if I really want to see results soon, say, in 10 years, I need to plant 1,312 trees.

OK! This looks awesome! I have enough land to plant a lot more than this, which means that I could squeeze in a few more offenses, such as:

  • Continue to travel long distance for a few more years (~1,200 trees)
  • My daughter’s lifetime flights (~2,500 trees)
  • My partner’s lifetime flights (~3,000 trees)
  • My stepson’s lifetime flights (~1,500 trees)
  • Our (3 people) other non-flight CO2-e (~6,000 trees)

Tree planting project, here I come!

A couple of departing thoughts:

  1. Trees add up! If we are to live carbon neutral via trees, we need a large piece of land just to offset the 4 of us! I don’t think this scales well for addressing climate change.
  2. I don’t necessarily trust third-party tree-planting carbon offset services out there to do the right thing. So if you’re considering planting trees as a carbon offset measure, make sure you really know how that is done.
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